Field of the Disclosure
Aspects of the present disclosure relate to a system, method and device to dynamically manage heat in an electric energy storage system, such as a battery pack or ultra-capacitor pack system in an electric vehicle.
Description of the Related Art
Electric powered vehicles for transportation offer reduction of harmful emissions in our environment, improved fuel economy and strengthened security of energy supply. It is well known in prior art that an electrical energy storage system is required to power electric vehicles. Other components that make up the rest of the drive system include traction motor(s) interfaced to the vehicle wheel system, high and low voltage power electronics, electrically powered accessories, system controls and vehicle interface.
Energy storage systems are created with a plurality of energy storage cells connected electrically to form a stack or module of cells configured in series or parallel to provide power and energy required for an application. Energy storage cells are typically battery cells. Depending on the power and energy granularity of the stack, there are stacks electrically connected in a system. In use under a typical charge/discharge duty cycle, the battery cells produce heat which must be controlled in order to maximize life of the elements and minimize the risk of thermal runaway. To optimize the safety, reliability, performance, active thermal management systems are often incorporated into the energy storage system. Active thermal management is generally accomplished by circulating a heat exchange fluid such as air or liquid or other media, using integrated HVAC units, or hybrid internal air circulation in conjunction with a water based chiller system, or Peltier thermal electric systems. Any HVAC system that is capable of adding or removing sufficient heat to an energy storage cell can be used with this present embodiment. Examples of different cooling circuit topologies in prior art used for thermal conditioning include liquid cooling loops to liquid air heat exchanger, air circulation, internal air circulation with air/water heat exchanger, dual cooling loops connected via a water heat exchanger are some commonly used topologies.
Prior to use, a battery system is thermally conditioned to some temperature value within the battery cell manufacturer's prescribed temperature range. Battery thermal preconditioning can be accomplished with logic that observes the ambient temperature during grid connected charging or charging from another source. The HVAC system draws power from the grid to heat the battery to an optimal temperature before charging begins. In cases when ambient temperatures are higher than the manufacturer's range, the charge control logic can cool the battery pack to desired levels before charging commences. For example, under charging scenario with low ambient temperatures, the vehicle's charge controller logic can activate a heating system interfaced to heat exchanger (4) via communication boundary (7). Under charge, pump (3) circulates fluid heated by the HVAC system connected to heat exchanger (4). In an alternate configuration an in line immersion heater is commonly incorporated into the thermal loop with various flow control devices. Prior art extends this concept to the occupants cabin of the vehicle, where pre-heating of the interior and pre-cooling of the interior is performed during charge to maximize drivers and passenger comfort and maximize vehicle range. Once the battery is preconditioned, the embodiment can be used to condition the battery if the vehicle is participating in a vehicle to grid application, or “V2G”, where the load center is the grid instead of the traction motor.
As an ESS is charged and discharged during use, heat is generated in the battery cells due to the cells internal resistances which ultimately results in a rise of temperature. If the heat is not rejected sufficiently fast or if the battery is allowed to operate outside of specified limits the battery will suffer reduced life, efficiency and performance, and ultimately fail. An active thermal management system is generally required to control the temperature so as to maintain the cell temperatures within an optimal temperature range. The optimal temperature range is normally prescribed by the energy storage cell manufacturer. Power is required to run the HVAC system which impacts the overall driving range and efficiency of the electric vehicle.
It is well known that battery life and capacity is extremely sensitive to temperature, requiring that the battery cells be operated within a well-defined temperature band. Conventional systems monitor every cell in a battery pack which increases packaging complexity and cost, and potential failure points. In addition, control methods have logic algorithms that are based on conservative threshold approach where corrective actions are based on readings that approach preset levels, which often result in an overshoot of target temperatures requiring aggressive compensation from the thermal management system, thus a reduction in efficiency. Such methods present the risk that operating limits are exceeded thus presenting a warranty issue with the battery cell supplier, reduced battery life, excess balancing required from the BMS due to thermal imbalances and swings.